A unique and highly sensitive chemical detection device can be created using guided-mode surface structure hologram optical filters as taught by Hobbs and Cowan in U.S. Pat. Nos. 6,791,757 and 6,870,624, both of which are incorporated herein by reference. Guided mode surface structure filters produce exceptionally narrow optical resonances that can be disturbed by the accumulation of material depositing on the structure surface. This disturbance is detected as a shift in the wavelength of the light resonating within the structural waveguide. The design of both reflection- and transmission-mode wave-guide resonant structures is further taught by Magnusson in U.S. Pat. Nos. 5,216,680, 5,598,300, and 6,154,480, and in the literature by Peng and Morris, “Resonant Scattering from two-dimensional gratings”, J. Opt. Soc. Am. A, Vol. 13, No. 5, p. 993, May 1996; Magnusson and Wang, “New Principle for optical filters,” Applied Physics Letters, 61, No. 9, p. 1022, August 1992; and Hobbs, “Laser-Line Rejection or Transmission Filters Based on Surface Structures Built on Infrared Transmitting Materials”, Proceedings SPIE Vol. 5786, Window and Dome Technologies and Materials IX, March 2005.
The utility of employing a surface structure resonator, or SSR, to detect the presence and concentration of organic chemicals has been demonstrated by Hobbs and Cunningham in U.S. Patent Application Publication Nos. 2002/0168295 and 2004/0132172, and by Cunningham in “Colorimetric resonant reflection as a direct biochemical assay technique”, Sensors and Actuators B, Vol. 81, 2002.
The wavelength of light that resonates in an SSR device is dependent on the angle of incidence of the light striking the SSR, and the SSR signal must be observed at a specific viewing angle, an angle equal to the angle of incidence of the interrogating light. To use an SSR to detect chemicals in an environment that is a large distance from the environment of the observer, an SSR sensor must be configured to operate on interrogating light that is incident at an angle very close to zero degrees, or normal to the SSR surface. In addition, the SSR is most commonly configured as a narrow-band reflector where the energy returned to the observer will be small compared to the energy in the broadband interrogating light beam. These considerations limit the practical use of an SSR to detect chemicals at distances of more than a few centimeters, and the use of inexpensive flexible materials such as plastic in the fabrication of SSR sensors.
Historically, applications of label-free sensors have relied primarily on bio-molecules such as antibodies, proteins, or nucleic acids. These biologically derived molecules tend to suffer from instability issues, which arise from sensitivity to changes in temperature, chemical environments, and the like. This invention provides for incorporation of robust, durable, selective capture agents such as molecularly imprinted polymers (MIPS) and other organic/inorganic molecules with selective affinity for target molecules.
Typical chemical and biochemical assays used for environmental monitoring require sample collection in the field, followed by field assays (utilizing portable instruments), or return of samples to a central facility for processing. Such assays cannot be performed in remote locations such as challenging terrain, aquatic environments, space, chemical reaction vessels, or bioreactors. Hence, there are practical limitations to the rate and scope of environmental vigilance, due to cost and logistical issues.
There remains an immediate need for a sensor device with the target selectivity and high sensitivity typical of an SSR that is capable of detecting the concentration of chemicals in an environment that is remote from the observer.